1. Field of the Invention
This invention relates to an improved electroconductive material for an electroconductive portion of a semiconductor device and, in particular, to a semiconductor device using an Si-bearing multi-component alloy for such an electroconductive portion.
2. Description of the Prior Art
As the electroconductive material of a semiconductor device, such as interconnection material and gate material, use has so far been made of aluminum, a polycrystalline silicon having a doped impurity, such as phosphorous, or a silicide of a metal element of Groups IV, V and VI in the Periodical Table, as represented by MoSi.sub.2, TiSi.sub.2.
The choice of such an electroconductive material for the interconnection material and gate material becomes more and more important in obtaining a high-speed unit of a high integration density. This is because the interconnection line on a semiconductor chip must be narrowed with a decrease in the size of the semiconductor device, with the result that the resistance in the electroconductive material forming the interconnection line is increased and thus the operation speed of the semiconductor device is largely affected. A high-temperature step is often employed in the process of manufacturing the semiconductor device, requiring a thermally and chemically stable electroconductive material.
An explanation will be given below in connection with the three conventional electroconductive materials as already set out above.
1. Aluminum
Aluminum is most popular as an electroconductive material and has a relatively low melting point, failing to withstand a high temperature atmosphere of above 1000.degree. C., for example, in a thermal diffusion step and annealing step following the injection of ions. Therefore, aluminum has a drawback in that it can be used only in a step of an interconnection between the lead wire and the bonding pad and a subsequent step and steps free from any high-temperature process.
2. Polycrystalline Silicon Doped with an Impurity
A polycrystalline silicon is most popular for use as an interconnection material and, when in practical use, has its resistivity lowered with an impurity such as phosphorus doped therein, because it has initially a high resistivity as in the case of insulation.
The electroconductive material is often used adjacent to the insulation as in the cases where, for example, the gate electrode of a MOS transistor is formed adjacent to the gate insulation film. In such a case, if the impurity such as phosphorus is doped in the polycrystalline silicon, it is diffused in the adjacent insulation, lowering the breakdown voltage of the insulation.
This drawback becomes more prominent due to a requirement of lowering the resistance level of the electroconductive material resulting from the narrowing of lines on the semiconductor chip, that is, due to the introduction of the impurity of a high concentration into the polycrystalline silicon. When the polycrystalline silicon is to be used as the electroconductive material, such impurity introducing step such as a diffusion step is necessary. From this viewpoint, much is desired to improve this aspect.
3. Silicide of Metal of Groups IV, V and VI
Where a silicide of a metal element of Groups IV, V and VI is deposited directly on the insulation, the silicon is diffused by a subsequent thermal step in the insulation or an interface between the insulation and the silicide is not flattened due to their reaction, thus lowering the breakdown characteristic of the semiconductor device. In order to solve this problem, a polycrystalline silicon layer must be formed at the boundary between the silicide and the insulation.